Synergistic Effect of Terminal Substitution and Central Core Extension Endowing the Organic Solar Cells with a...

This work focuses on how the structural regulation of nonfullerene acceptors (NFAs) improves the power conversion efficiency (PCE) of organic solar cells through terminal substitution and central core extension. Three series of NFAs (DONAD-X, DPT-X, and DOYAD-NO₂) are designed by introducing different strong electron-withdrawing terminal substituents (X) and extended conjugated central cores (Y). High-precision density functional theory (DFT) and time-dependent DFT calculations are employed to comprehensively investigate their ground-state and excited-state properties. The calculation results reveal that strong electron-withdrawing terminal substituents are beneficial for NFA to effectively reduce the molecular energy gap, broaden the absorption spectrum, and increase the electron mobility. Symmetric substitution is more effective than asymmetric substitution in achieving longer maximum absorption wavelength and smaller excitation energy. The introduction of symmetric terminal substitution and synergistic effect of both -CN and -NO₂ groups (abbr -CNO₂) enables NFA to achieve optimal performance. Furthermore, the extended conjugated central cores effectively enhance the chemical reactivity and intramolecular charge transfer (ICT) of the NFAs. Based on the selection of the optimal terminal substituent and central core, we construct the most promising acceptor DOIAD-CNO₂ and find that the PM6/DOIAD-CNO₂ interface possesses the largest short-circuit current density and PCE (16.39%). The CT mechanisms of the designed PM6/NFA interfaces involve the coexistence of hot exciton excitation, intermolecular electric field, and direct excitation, which can promote more exciton separation. PM6/DOIAD-CNO₂ has the most CT and FE/CT states with larger oscillator strengths, thereby obtaining the largest PCE. This work can inspire the experimental synthesis and application of these acceptor candidates and provide guidance for further design and development of more efficient NFAs.